MR angiography with an ultrasmall superparamagnetic iron oxide blood pool agent

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Abstract
The purpose of the study was to investigate the use of a dextran‐coated ultrasmall superparamagnetic iron oxide (USPIO) as a blood pool contrast agent for thoracic and abdominal MR angiography. Abdominal and thoracic MR angiography was performed in six healthy volunteers using two‐dimensional and three‐dimensional spoiled gradient echo (SPGR) sequences before and after intravenous administration of USPIO. Doses ranged from 1.1 to 2.6 mg Fe/kg. Flip angle was varied from 20 to 60°. Subjective image quality, analysis of signal‐to‐noise ratio (SNR), and blood T1 relaxation times were measured. USPIO significantly lowered the T1 of blood (from 1,210 ms precontrast to 159 ms postcontrast at a dose of 2.6 mg Fe/kg) (P < .01). Image quality on coronal fast three‐dimensional breath‐hold SPGR images of the abdomen increased with increasing dose and was maximum at the highest dose, producing an aortic SNR of 9.6 compared to 1.8 precontrast. Axial two‐dimensional time‐of‐flight (TOF) aortic SNR was reduced significantly from 13 on precontrast to 6 on the postcontrast images at the highest dose (P < .05) due to T2* shortening effects. There was little flip angle dependence on image quality. Due to the T1 shortening effect and long intravascular half‐life, USPIO improved visualization of vascular anatomy using three‐dimensional fast SPGR imaging. The echo time must be minimized to minimize signal loss from T2* shortening effects. The blood pool distribution of USPIO is useful for equilibriumphase MR angiography.